tests: Avoid single-shot environment export for shell function invocation

Some shells have issues with a single-shot environment variable export
when invoking a shell function.  This fixes the ones I found that invoke
test_must_fail that way.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

t/t3409-rebase-hook.sh

@@ -118,7 +118,11 @@ test_expect_success 'pre-rebase hook stops rebase (1)' '
 test_expect_success 'pre-rebase hook stops rebase (2)' '
 	git checkout test &&
 	git reset --hard side &&
-	EDITOR=true test_must_fail git rebase -i master &&
+	(
+		EDITOR=:
+		export EDITOR
+		test_must_fail git rebase -i master
+	) &&
 	test "z$(git symbolic-ref HEAD)" = zrefs/heads/test &&
 	test 0 = $(git rev-list HEAD...side | wc -l)
 '

t/t3412-rebase-root.sh

@@ -172,14 +172,22 @@ EOF
 
 test_expect_success 'pre-rebase hook stops rebase' '
 	git checkout -b stops1 other &&
-	GIT_EDITOR=: test_must_fail git rebase --root --onto master &&
+	(
+		GIT_EDITOR=:
+		export GIT_EDITOR
+		test_must_fail git rebase --root --onto master
+	) &&
 	test "z$(git symbolic-ref HEAD)" = zrefs/heads/stops1
 	test 0 = $(git rev-list other...stops1 | wc -l)
 '
 
 test_expect_success 'pre-rebase hook stops rebase -i' '
 	git checkout -b stops2 other &&
-	GIT_EDITOR=: test_must_fail git rebase --root --onto master &&
+	(
+		GIT_EDITOR=:
+		export GIT_EDITOR
+		test_must_fail git rebase --root --onto master
+	) &&
 	test "z$(git symbolic-ref HEAD)" = zrefs/heads/stops2
 	test 0 = $(git rev-list other...stops2 | wc -l)
 '
@@ -224,7 +232,11 @@ test_expect_success 'rebase --root with conflict (second part)' '
 
 test_expect_success 'rebase -i --root with conflict (first part)' '
 	git checkout -b conflict2 other &&
-	GIT_EDITOR=: test_must_fail git rebase -i --root --onto master &&
+	(
+		GIT_EDITOR=:
+		export GIT_EDITOR
+		test_must_fail git rebase -i --root --onto master
+	) &&
 	git ls-files -u | grep "B$"
 '
 
@@ -262,7 +274,11 @@ EOF
 
 test_expect_success 'rebase -i -p --root with conflict (first part)' '
 	git checkout -b conflict3 other &&
-	GIT_EDITOR=: test_must_fail git rebase -i -p --root --onto master &&
+	(
+		GIT_EDITOR=:
+		export GIT_EDITOR
+		test_must_fail git rebase -i -p --root --onto master
+	) &&
 	git ls-files -u | grep "B$"
 '